Pulse voltage age acceleration of a laser for determining reliability

ABSTRACT

A method of accelerating the aging of a laser to thereby determine the reliability of the laser. The method includes an act of providing a laser die for reliability testing, an act of applying a plurality of short signal pulses to the laser die so as to simulate the aging of the laser die, and an act of ascertaining the reliability of the laser die based on its response to the plurality of short signal pulses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/941,215, filed May 31, 2007, which is incorporated herein byreference in its entirety.

BACKGROUND

Semiconductor lasers are currently used in a variety of technologies andapplications, including communications networks. One type ofsemiconductor laser is the distributed feedback (“DFB”) laser. The DFBlaser produces a stream of coherent, monochromatic light by stimulatingphoton emission from a solid state material. DFB lasers are commonlyused in optical transmitters, which are responsible for modulatingelectrical signals into optical signals for transmission via an opticalcommunication network.

Generally, a DFB laser includes a positively or negatively doped bottomlayer or substrate, and a top layer that is oppositely doped withrespect to the bottom layer. An active region, bounded by confinementregions, is included at the junction of the two layers. These structurestogether form the laser body. A grating is included in either the top orbottom layer to assist in producing a coherent light beam in the activeregion. The coherent stream of light that is produced in the activeregion can be emitted through either longitudinal end, or facet, of thelaser body. DFB lasers are typically known as single mode devices asthey produce light signals at one of several distinct wavelengths, suchas 1,310 nm or 1,550 nm. Such light signals are appropriate for use intransmitting information over great distances via an opticalcommunications network.

BRIEF SUMMARY

One example disclosed herein relates to a method of accelerating theaging of a laser to thereby determine the reliability of the laser. Themethod includes an act of providing a laser die for reliability testing,an act of applying a plurality of short signal pulses to the laser dieso as to simulate the aging of the laser die, and an act of ascertainingthe reliability of the laser die based on its response to the pluralityof short signal pulses.

Another example disclosed herein relates to a method of accelerating theaging of multiple lasers to thereby determine the reliability of thelasers. The method includes an act of providing a first plurality oflasers for reliability testing, wherein the first plurality of lasersinclude a first facet coating, an act of applying a plurality of shortsignal pulses to the first plurality of lasers so as to simulate theaging of the first plurality of lasers, an act of ascertaining thereliability of the first plurality of lasers based on their response tothe plurality of short signal pulses, an act of providing a secondplurality of lasers for reliability testing, wherein the secondplurality of lasers include a second facet coating that is differentfrom the first facet coating, an act of applying a plurality of shortsignal pulses to the second plurality of lasers so as to simulate theaging of the second plurality of lasers, and an act of ascertaining thereliability of the second plurality of lasers based on their response tothe plurality of short signal pulses.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

Additional features and advantages will be set forth in the descriptionwhich follows, and in part will be obvious from the description, or maybe learned by the practice of the teaching herein. The features andadvantages of the teaching herein may be realized and obtained by meansof the instruments and combinations particularly pointed out in theappended claims. These and other features will become more fullyapparent from the following description and appended claims, or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only illustrated embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 is a perspective view of an optical transceiver module thatserves as one exemplary environment in which embodiments of the presentinvention can be practiced;

FIG. 2 is a cross sectional side view of an epitaxial base portion of adistributed feedback (“DFB”) laser, according to one embodiment of thepresent invention;

FIG. 3 is a progressive view of various processing and manufacturestages performed on the epitaxial base portion shown in FIG. 2;

FIG. 4 illustrates a short signal pulses being applied to a laser inaccordance with embodiments disclosed herein;

FIG. 5 illustrates a flowchart of a method for accelerating the aging ofa laser to thereby determine the reliability of the laser in accordancewith embodiments disclosed herein;

FIG. 6 illustrates a flowchart of a method for accelerating the aging ofmultiple lasers to thereby determine the reliability of the lasers inaccordance with embodiments disclosed herein;

FIG. 7 illustrates output power versus thermal roll-over in accordancewith embodiments disclosed herein;

FIG. 8 illustrates output power and optical intensity versus COD levelin accordance with embodiments disclosed herein; and

FIG. 9 illustrates COD level versus aging in accordance with embodimentsdisclosed herein.

DETAILED DESCRIPTION

Reference will now be made to figures wherein like structures will beprovided with like reference designations. It is understood that thedrawings are diagrammatic and schematic representations of presentlypreferred embodiments of the invention, and are not limiting of thepresent invention nor are they necessarily drawn to scale.

Example Operating Environment

Reference is first made to FIG. 1, which depicts a perspective view ofan optical transceiver module (“transceiver”), generally designated at100, for use in transmitting and receiving optical signals in connectionwith an external host that is operatively connected in one embodiment toa communications network (not shown). As depicted, the transceiver shownin FIG. 1 includes various components, including a receiver opticalsubassembly (“ROSA”) 10, a transmitter optical subassembly (“TOSA”) 20,electrical interfaces 30, various electronic components 40, and aprinted circuit board (“PCB”) 50. In detail, two electrical interfaces30 are included in the transceiver 100, one each used to electricallyconnect the ROSA 10 and the TOSA 20 to a plurality of conductive pads 18located on the PCB 50. The electronic components 40 are also operablyattached to the PCB 50. An edge connector 60 is located on an end of thePCB 50 to enable the transceiver 100 to electrically interface with ahost (not shown here). As such, the PCB 50 facilitates electricalcommunication between the ROSA 10/TOSA 20, and the host. In addition,the above-mentioned components of the transceiver 100 are partiallyhoused within a shell 70. Though not shown, the shell 70 can cooperatewith a housing portion to define a covering for the components of thetransceiver 100.

While discussed in some detail here, the optical transceiver 100 isdescribed by way of illustration only, and not by way of restricting thescope of the invention. As mentioned above, the optical transceiver 100in one embodiment is suitable for optical signal transmission andreception at a variety of per-second data rates, including but notlimited to 1 Gbit, 2 Gbit, 2.5 Gbit, 4 Gbit, 8 Gbit, 10 Gbit, or higherrates. Furthermore, the principles of the present invention can beimplemented in optical transmitters and transceivers of shortwave andlong wave optical transmission and any form factor such as XFP, SFP andSFF, without restriction.

The TOSA 20 of the transceiver 100 is one example of an opticaltransmitter that can employ an optical source, such as a semiconductorlaser, that is configured according to embodiments of the presentinvention. Briefly, in operation the transceiver 100 receives electricalsignals from a host (not shown) or other data signal-producing device towhich the transceiver is operably connected for transmission onto anoptical fiber operably connected to the TOSA 20. Circuitry of thetransceiver 100 drives a laser (described below) within the TOSA 20 withsignals that cause the TOSA to emit onto the optical fiber opticalsignals representative of the information in the electrical signalprovided by the host. Accordingly, the TOSA 20 serves as anelectro-optic transducer. Having described a specific environment withrespect to FIG. 1, it will be understood that this specific environmentis only one of countless architectures in which the principles of thepresent invention may be employed. As previously stated, the principlesof the present invention are not intended to be limited to anyparticular environment.

Example Distributed Feedback Laser

A distributed feedback (“DFB”) laser is one example of a semiconductoroptical device employed according to embodiments of the presentinvention. By way of general overview, a DFB laser contains a cavityhaving an active medium and a distributed reflector that operates in awavelength range of the laser action. The DFB laser has multiple modes,including both longitudinal and transversal modes, but one of thesemodes will typically offer better loss characteristics relative to theother modes. This single mode typically defines a single-frequencyoperation of the DFB laser.

The following description provides various details regarding a tengigabit/second (“10G”) DFB laser configured for light emission at awavelength of approximately 1310 nm. The following description includesboth structural and functional characteristics of the 10G DFB laser,together with certain details regarding the manufacturing processes usedto build the laser. Note, however, that this description is meant to beexemplary only; indeed, lasers and other semiconductor optical deviceshaving structural and/or functional aspects that differ from the presentdescription can also benefit from the principles of embodiments of thepresent invention as disclosed herein. It is also appreciated thatadditional or alternative layers, layer thicknesses, or structures canbe incorporated into the present laser device as will be understood bythose of skill in the art. The following discussion is therefore notintended to limit the present invention in any way. In particular, theprinciples of the present invention may also be achieved in a 1310 nm2.5G DFB laser.

a. Base Epitaxial Layers

FIG. 2 illustrates the base epitaxial layers of an example 10G DFBlaser, generally designated at 110, at a stage prior to etching of thegrating layers. The DFB laser 110 is grown on an Indium Phosphidesubstrate (n-InP substrate) 114.

A “mode modifier” layer (n-IGAP Mode Modifier) 118 is grown on top ofthe substrate 114 using Indium Gallium Arsenide Phosphide at anapproximate thickness of 120 nm. This layer functions to reduce thepower of second-order transversal modes that propagate within the laserstructure. In particular, the mode modifier layer 118 effectivelyincreases the loss associated with these second-order transverse modesand couples the modes away from the gain medium of the laser. Thissuppression of second-order transverse modes allows for wider mesawidths on the laser because the laser is less sensitive to these modes.

A buffer layer (n-InP) 122 is made of Indium Phosphide and grown on topof the “mode modifier” layer 118. This buffer layer is approximately 1.4μm thick and provides a surface on which the n-layers of the laser aregrown.

A first n-confinement layer 126 of Aluminum Indium Arsenide (n-MA) isgrown at a thickness of approximately 20 nm on the buffer layer and isdoped with silicon. A second n-confinement layer 130 of Aluminum GalliumIndium Arsenide (n-AGIA SCH) is grown at a thickness of 30 nm on then-MA layer and is also doped with silicon. Both of these layers arecurrent confinement layers and effectively maintain electrons within thelaser active region so that photons are produced. The n-AGIA SCH secondn-confinement layer 130 is graded to improve the confinementcharacteristics of the layer. The thicknesses of these n-layers weredesigned to be thin in order to optimize the thermal performance of thelaser.

A multi-quantum well active region (MQW region) 134 is grown on then-type confinement layers. In this example, the active region 134 isdesigned to have eight wells 136 with corresponding wavelengths of ˜1295nm. Quantum barriers 138 between the wells have correspondingwavelengths of approximately 980 nm. Standard barrier wavelengths are inthe range of 1060-1090 nm and thus have smaller barrier heights thantypical multi-quantum-well designs. The depth and width of the wells aredesigned to produce a 1310 nm photon. The active region is designed tobe “strain compensated” which means that the barriers are designed tohave opposing strain characteristics relative to the well straincharacteristics. As a result, the strain generated from the barriers atleast partially cancels the strain generated by the wells and reducesthe overall strain on the layer. In the illustrated embodiment, quantumwell design may be manufactured so that a complete cancellation ofstrain does not occur, but a small amount of strain remains forperformance reasons.

In addition, the layers of the MQW region 134 are intentionally dopedwith Zn, to maintain a low-level p-type doping. This is done to assurethat the p-n junction of the laser diode always occurs in the sameplace, and is not made variable by unpredictable dopant diffusionprocesses. Further details regarding the doping of the MQW region 134will be given further below.

A first p-confinement layer 142 of Aluminum Gallium Indium Arsenide(p-AGIA SCH) is grown on the active region at a predetermined thicknessand is doped with zinc. A second p-confinement layer 146 of AluminumIndium Arsenide (p-MA) is grown at a predetermined thickness, on thep-AGIA SCH layer and is also doped with zinc. Both of the p-layers areconfinement layers and effectively maintain holes within the activeregion so that photons are produced. The p-AGIA SCH layer 142 is gradedto improve the confinement characteristics of the layer.

A spacer layer 150 is located above the p-confinement layers. Thisspacer layer is made of Indium Phosphide. Various “above-active” gratinglayers are located above the spacer layer. An etch stop layer (p-IGAPetch stop) 152 made of Indium Gallium Arsenide Phosphide is grown on thespacer layer 150. This etch stop layer is provided for stopping the mesaetch during the regrowth process.

A second spacer layer 156 is provided to separate the etch stop layer152 and the grating layer. In the illustrated design, the grating etchstep is timed to stop within this spacer layer. The layer is made ofIndium Phosphide (p-InP).

A grating layer (p-IGAP) 160 is grown on the second spacer layer 156 andis made of Indium Gallium Arsenide Phosphide. The grating layer is“above active” (as compared to other possible designs in which thegrating is below the active region). Laser holography, wet etching, andsubsequent InP regrowth, as explained further below, are used to createa uniform grating, consisting of alternating layers of high index IGAPand low index InP down the length of the laser cavity.

The laser cavity of the example DFB laser 110 can support two degeneratelongitudinal grating modes because the grating formed in the gratinglayer 160 is uniform (as opposed to, e.g., a quarter-wave shifteddesign). Selection of one or the other of these two modes is dependentupon the phase associated with the facet cleave, which is dependent uponthe location of the cleave with respect to the grating period. Becausethe location of the cleave cannot be controlled with sufficientprecision, all phase possibilities will be represented by any ensembleof devices of this design. As a result, there will always be a finitepercentage of laser parts for which both grating modes are equallysupported, resulting in inadequate single-mode behavior. These lasersare discarded and not sold.

A top layer 162 is provided above the grating layer on which regrowth ofother layers is performed.

b. Grating Fabrication and Regrowth

FIG. 3 illustrates various grating fabrication and subsequent regrowthstages employed in forming portions of the structure of the DFB laser110. In particular, FIG. 3 shows a side view of the base epitaxialstructure 112 of FIG. 2, together with subsequent grating fabricationand regrowth steps in forming the DFB laser 110. As described above andby way of brief overview, a wet etch is performed to etch periodic gapswithin the grating layer, as shown in FIG. 3. After the etch iscompleted and the grating teeth are created, thick Indium Phosphide isgrown (“regrowth”) on the etched, base epitaxial structure, in order tofill the gaps with low-index InP and also to form the mesa layer, alsoshown in FIG. 3. The regrowth is completed with an Indium GalliumArsenide layer for electrical contact.

As mentioned above, the Indium Phosphide regrowth is used to create amesa on the epitaxial base that provides current confinement and alsofunctions as a waveguide, by virtue of lateral optical confinement. Thisstructure is also referred to herein as a “ridge waveguide” structure.Photoresist is used to etch ridges on the regrowth, thereby defining themesa of the DFB laser. Both dry and wet etching can be used in creatingthe mesa ridges.

After the etching process is complete, a dielectric layer (notexplicitly shown) is placed on the structure. In the present design, a“triple stack” of Silicon Nitride, Silicon Dioxide, and Silicon Nitrideis used as the dielectric. This layer is typically thick in order toreduce parasitic capacitance (and improve speed) and is used to confinethe current within the mesa. In other embodiments, a single layer ofSilicon Nitride or Silicon Oxide can be employed for the dielectriclayer.

The dielectric layer is removed from the top of the mesa to allow anelectrical contact and metallic layer (not shown) to be placed on themesa. Electrical contact is made by depositing metal onto the IndiumGallium Arsenide layer at the top of the mesa. This contact is both anon-alloy contact and a low penetration contact.

A metallic layer (not shown) is placed on the electrical contact towhich electrical current may be provided to the laser structure. In thepresent embodiment, the metallic layer is made of three sub-layers oftitanium, platinum and gold. The titanium sun-layer is placed directlyon the electrical contact layer, then the platinum sub-layer and goldsub-layer are applied. This metallic layer provides sufficientconductivity to the Indium Gallium Arsenide layer so that current can beproperly provided to the laser structure.

Bottom electrical contacts are generated by thinning the InP substrateand placing an n-type metallic layer (not shown) on the bottom.

A DFB laser is removed from a wafer using common techniques by cleavingand breaking the wafer both horizontally and laterally to separate eachlaser. After this process, anti-reflective (“AR”) and high-reflective(“HR”) coating processes are performed to encapsulate the active regionof the laser and provide the requisite reflectivity characteristics ofthe laser cavity. The reflectivity characteristics define the opticalpower emitted from the back of the laser and the front of the laser. Inuniform grating designs, a majority of the optical power is emitted fromthe front of the laser which optically couples with an optical fiber. Aminority of the optical power is emitted from the back of the laser,which may couple with a photodetector (not shown) that is used tomonitor laser performance.

In one embodiment, the AR and HR coatings are made of layers of SiliconOxide and Silicon. The reflectivity of the AR coating is designed to beless than about 0.5%, while the HR coating is designed to be higher thanapproximately 90%. Once the coating process is complete, a testingprocess is performed in which the power characteristics and opticalspectrum are tested.

The DFB laser 110 and photodetector are packaged into an opticalsub-assembly, such as the TOSA 20 shown in FIG. 1, which is subsequentlypackaged into an optical module, e.g., the transceiver 100 of FIG. 1,along with driver and control integrated circuits.

Although the above description was specifically tailored to a DFB laser,the examples disclosed herein may also be used in other high-speedlasers, such as a 1310 nm 10G Fabry-Perot (FP) laser. The Fabry Perotlaser, as is known in the art, is also grown on a substrate with variouslayers, a mesa and an active.

c. Burn-In of a RWG Laser

Typically, every wafer that is fabricated generates a number offunctionally good laser die. In one example, a launched wafer mayprovide 2000 good laser die. Not all of these 2000 laser die, however,are robust enough to withstand aging in a user's hands. A harsh stresscondition called burn-in, which is a combination of temperature, currentand power, is generally used to weed-out the weak sub-population oflaser die. After weeding out the weak sub-population, the rest of theparts can be shipped to an end user. Unfortunately, however, there areat least two challenges associated with identifying a suitable burn-incondition, particularly for aluminum ridge waveguide lasers.

One challenge is that with a continuous wave (CW) stress condition,finding an optimal combination of stress conditions (temperature,current, power) may be impossible. Generally a RWG laser or other typeof laser can only safely operate well below a critical optical intensitylevel called Catastrophic Optical Damage (COD) threshold intensity. Whena laser is operated at or above this intensity level, the laser diescatastrophically. The COD intensity level is determined by the materialcomposition of the laser, by the material composition of any facetcoating material that has been applied to the laser, and the effectivecross-sectional area of the output beam of the laser. It is also wellknown that the COD level decreases with age of the laser and the agingconditions (eg: power) under which the laser has been aged.

The weaker population of lasers mentioned above typically tend to havelower COD levels. Under CW operating conditions, the maximum outputpower is limited by thermal roll-over as seen in FIG. 7. This maximumoutput power and optical intensity may be less than the COD level andhence will hinder a manufacturer's ability to screen out the weakdevices as seen in FIG. 8. Under a pulsed-mode operation the laser canreach high optical intensity since it does not experience thermalroll-over. Thus, the weaker population of laser die, which have a lowerCOD level, will die during this pulsed-mode stress and hence, can beweeded out, as also seen FIG. 8.

The second challenge is that under CW mode the duration needed to weedthe weaker population, even if it were feasible, would be long. Thisleads to significant up-front capital investment and hence is notdesirable. On the contrary, with pulsed mode, a higher stress conditioncan be explored leading to a very short and desirable burn-in.

d. Reliability Testing of a Laser

Typically, reliability of a laser is checked by applying current for aspecified time, for example at a time scale of 500-1,000 hours. Theperformance of the laser may then be checked. In addition, the laser maybe placed in an oven at 100 degrees Celsius for the specified time whilethe current is applied the laser.

In some tests, a large group of lasers are subjected to reliabilitytesting at the same time. For example, in one embodiment, a first groupof 100 lasers with a first type of facet coating may have a currentapplied to them for a specified time and/or may be placed in an oven toage them. In like manner, a second grouping of 100 lasers with a secondfacet coating may be tested for reliability.

One of the challenges with reliability, particularly for aluminum ridgewaveguide lasers, is that this process takes a long time to figure outwhat the laser's reliability is. It generally costs a lot of money inupfront investment and a lot of parts for a long time duration astypically the lasers have to age by using different ovens and operatingunder different conditions.

Advantageously, the principles of the present invention allow for atesting method that is configured to test the reliability of a laser ina very short period of time. For example, as is illustrated in FIG. 4, aseries of short pulses 410 and/or 420 may be applied in short successionto a laser 400 such as the laser 110 described in relation to FIGS. 1-3.Of course, the principles of the present invention are not limited toDFB lasers and may be applied to other types of lasers such as VCSELS,FP and other types of lasers known in the art. The series of shortpulses 410 and 420 have the effect of rapidly aging the laser undertest. The laser's reliability may then quickly be ascertained. Inaddition, the series of short pulses aids in determining the weakersubset of laser die discussed previously and thus helps a manufacturerto subsequently weed-out theses lasers from the more robust subset oflaser die.

For example, as illustrated in FIG. 4, pulse 410 may have an amplitudeA, a width W, and a period T. In some embodiments, the width of thepulse may be less than or equal to about 2 milliseconds, although otherwidths may also be used as circumstances warrant. Likewise pulse 420 mayalso have an amplitude A, a width W, and a period T.

In one embodiment, the amplitude and width of pulse 410 and/or pulse 420may be the same. In another embodiment, the amplitude of pulse 410and/or pulse 420 may be varied while the width is fixed or keptconstant. In still other embodiments, the width of pulse 410 and/orpulse 420 may be varied while the amplitude is fixed or kept constant.In yet further embodiments, the amplitude and width of pulse 410 and/orpulse 420 may both be varied.

In one embodiment, pulse 410 may be a 2000 volt pulse while pulse 420may be a −2000 volt pulse. It should be noted that FIG. 4 shows that anynumber of pulses may be used as necessary and thus the embodimentsdisclosed herein are not limited by any number of pulses. The amount ofcurrent that finally causes the laser under test to fail may then beascertained.

Typically, as current is injected into a laser, the laser heats up andthe output optical power may not correspond to the amount of inputcurrent due to this heat. Use of the short pulses, however, typicallyallows a larger amount of current to be injected into the laser undertest and a larger amount of optical power to be output without the lossdue to the heat, which in turn advantageously allows for greaterreliability testing.

In one embodiment, the series of pulses 410 and/or 420 may first beapplied to a first set of lasers, such as a group of 100 lasers, with afirst facet coating. The current levels and optical output levels atwhich the laser begin to fail may then be ascertained. This process maybe continued until all the lasers have failed. Accordingly, a range ofoperating currents at which the lasers fail may be determined.

In similar fashion, a second set of lasers, such as a group of 100lasers, with a second facet coating may be have pulses 410 and/or 420applied to them. The current levels and the optical output levels atwhich these lasers begin to fail may also be ascertained and the rangeof currents may be determined. Further, the two types of facet coatingsmay be compared to determine which facet coating caused their respectiveplurality of lasers to be operate for a longer period of time.

Advantageously, the use of short pulses 410 and/or 420 also allow for aquick test of the COD level of a laser or group of lasers under test. Asexplained above, the use of the pulses allows for an increasing amountof current to be injected into the laser and a greater optical intensityto be output. The point at which the laser reaches or exceeds the CODlevel and fails may then be ascertained quickly, efficiently, and withlower cost as may be seen in FIG. 9.

Referring now to FIG. 5, a flowchart of a method 500 for acceleratingthe aging of a laser to thereby determine the reliability of the laseris illustrated. Method 500 includes an act of providing a laser die forreliability testing (act 502). For example, a laser such as laser 110 ofFIG. 2, or any other suitable laser, may be provided for reliabilitytesting.

Method 500 also includes an act of applying a plurality of short signalpulses to the laser die so as to simulate the aging of the laser die(act 504). For example, as described previously, a number of shortsignal pulses, such as positive and negative 2000 volt signals, may beapplied to the laser provided for in act 502.

Method 500 further includes an act of ascertaining the reliability ofthe laser die based on its response to the plurality of short signalpulses (act 506). For example, as described previously, the short pulsesrapidly age the laser under test. The laser's reliability may thenquickly be ascertained. In other words, operational information aboutthe laser may be ascertained quickly. Advantageously, this removes theneed for the typical long, expensive process of aging the laser byputting it in an oven to test its reliability. Instead, the amount ofcurrent that causes a laser to fail over time and its COD may be quicklyascertained.

Referring now to FIG. 6, a flowchart of a method 600 for acceleratingthe aging of multiple lasers to thereby determine the reliability of thelasers is illustrated. Method 600 includes an act of providing a firstplurality of lasers for reliability testing, wherein the first pluralityof lasers include a first facet coating (act 602), an act of applying aplurality of short signal pulses to the first plurality of lasers so asto simulate the aging of the first plurality of lasers (act 604) and anact of ascertaining the reliability of the first plurality of lasersbased on their response to the plurality of short signal pulses (act606). For example, a short series of pulses may be applied to a firstset of lasers such as laser 110 or some other suitable laser thatinclude a first facet coating to simulate the aging of the lasers. Thereliability of the first set of lasers may then be determined aspreviously described.

Method 600 also includes an act of providing a second plurality oflasers for reliability testing, wherein the second plurality of lasersinclude a second facet coating that is different from the first facetcoating (act 608), an act of applying a plurality of short signal pulsesto the second plurality of lasers so as to simulate the aging of thesecond plurality of lasers (act 610), and an act of ascertaining thereliability of the second plurality of lasers based on their response tothe plurality of short signal pulses (act 612). For example, a shortseries of pulses may be applied to a second set of lasers such as laser110 or some other suitable laser that includes a second facet coatingthat is different from the first facet coating to simulate the aging ofthese lasers. The reliability of the second set of lasers may then bedetermined as previously described. In some embodiments, the two typesof facet coatings may be compared to determine which facet coatingcaused their respective plurality of lasers to be operated for a longerperiod of time.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method of accelerating the aging of a laser to thereby determinefailure of the laser, the method comprising: providing a laser structurehaving electrical contacts; providing a current source configured forsupplying current in a plurality of short signal pulses; applyingcurrent from the current source to the laser structure such that thelaser structure emits an output light beam having an output power andoptical intensity, the current being applied to the laser structure in aplurality of short signal pulses so as to simulate the aging of thelaser structure; and ascertaining failure of the laser structure inresponse to the plurality of short signal pulses of current.
 2. Themethod in accordance with claim 1, wherein the plurality of short signalpulses comprise a positive 2000 volt pulse and/or a negative 2000 voltpulse.
 3. The method in accordance with claim 1, wherein ascertainingfailure of the laser structure comprises: determining the amount ofcurrent that causes the laser structure to become inoperable.
 4. Themethod in accordance with claim 1, wherein ascertaining failure of thelaser structure comprises: determining the Catastrophic Optical Damage(COD) threshold intensity of the laser structure.
 5. The method inaccordance with claim 1, wherein the plurality of short signal pulsesinclude an amplitude and a width that are the same.
 6. The method inaccordance with claim 1, wherein the plurality of short signal pulsesinclude an amplitude that is varied and a width that is fixed.
 7. Themethod in accordance with claim 1, wherein the plurality of short signalpulses include a width that is varied and an amplitude that is fixed. 8.The method in accordance with claim 1, wherein the plurality of shortsignal pulses include an amplitude and a width that are both varied. 9.The method in accordance with claim 1, wherein ascertaining failure ofthe laser structure comprises: an act of ascertaining if the laserstructure is part of a subset of weaker laser structures of a group oflaser structures from a wafer.
 10. The method in accordance with claim1, wherein the laser structure is a Fabry-Perot (FP) laser.
 11. Themethod in accordance with claim 1, wherein the laser structure is a DFBlaser.
 12. The method in accordance with claim 11, wherein the laserstructure comprises: a substrate; a mode modifier layer positioned abovethe substrate; a buffer layer positioned above the mode modifier layer;a first confinement layer positioned above the buffer layer; a secondconfinement layer positioned above the first confinement layer and belowan active region; a third confinement layer positioned above the activeregion; a fourth confinement layer positioned above the thirdconfinement layer; a first spacer layer positioned above the fourthconfinement layer; an etch stop layer positioned above the first spacerlayer; a second spacer layer positioned above the etch stop layer; agrating layer positioned above the second spacer layer; and a top layerpositioned above the grating layer and below a mesa.
 13. The method inaccordance with claim 1, comprising: providing a plurality of laserstructures including the laser structure, each laser structure beingfrom a single wafer and having electrical contacts; providing a currentsource configured for supplying current in a plurality of short signalpulses; applying current from the current source to the plurality oflaser structures such that each of the laser structures emit an outputlight beam having an output power and optical intensity, the currentbeing applied to each of the laser structures in a plurality of shortsignal pulses so as to simulate the aging of the plurality of laserstructures; and identifying a sub-population of laser structures of theplurality that fail before other laser structures of the plurality. 14.The method in accordance with claim 13, comprising determining a rangeof operating currents at which the laser structures of the pluralityfail.
 15. The method in accordance with claim 13, comprising: discardingthe sub-population of laser structures that failed.
 16. The method inaccordance with claim 1, wherein each pulse has a width less than orequal to about 2 milliseconds.
 17. The method in accordance with claim1, wherein the plurality of short signal pulses of current results in alarger amount of current to be applied to the laser structure comparedto a continuous wave.
 18. The method in accordance with claim 17,wherein the plurality of short signal pulses of current results in lessheat to be applied to the laser structure compared to a continuous wave.19. The method in accordance with claim 17, wherein the plurality ofshort signal pulses of current results in a larger amount of opticalpower output from the laser structure compared to a continuous wave. 20.The method in accordance with claim 1, wherein the method is devoid of:heating the laser structure in an oven; and/or causing thermalroll-over.